Purification of sugar solutions



. molasses.

Patented Oct. 30, 1945.

UNITED STATE PURIFICATION OF SUGAR SOLUTIONS Abraham Sidney Behrman,Chicago, Ill., auignor to Infilco Incorporated, a corporation of Dela-No Drawing. Application April 27, 1940, Serial No. 331,931

12 Claims. (Cl. 1279-55) This invention relates to the purification ofaqueous sugar solutions and similar aqueous liquids, and is concernedprimarily with improvements in the production of sucrose, dextrose andthe like.

A principal object of the invention is an improvement in methods forpurifying solutions of sucrose, particularly those obtained from sugarbeets and from sugar cane.-

Another object of the invention is to provide an improvement in themanufacture of dextrose, particularly corn sugar.

Another object of the invention is an improvement in the production ofsugars of increased purity and diminished ash constituents.

Other objects of the invention will become apparent on the furtherreading of this specification and the appended claims.

In the manufacture of commercial sugars from practically any source itis highly desirable that the non-sugar constituents be kept or reducedas low as possible in order to improve the quality and increase theyield of crystallizable sugar and to decrease the amount of residuallow-value Even in the production of the modern so-called liquid sugars,which are sold as concentrated syrups, without crystallization of solidsugar, a correspondingly high degree of purity is usually required.

. It is in the production of the solid sugars, however, that the purityof the sugar juices is of most obvious importance since it bears adirect relation to the quality of sugar and the amounts of the variousgrades of sugar and of molasses which are the primary factors in theoperation and economy of a sugar mill or plant. These factors andrelationships are well understood by those skilled in the sugar art, andso need not be given more than brief mention here.

The non-sugar constituents of raw sugar Juices may be either organic orinorganic. Usually they procedures may still contain inorganic ashconstituents to the extent of 2000 to 5000 parts per million, consistingmostly of potassium and sodium compounds several of which have beenshown to be highly melassigenic. The remaining organic non-sugars andmetal salts of organic acids also contribute to the formation ofmolasses, in addition to which may may seriously affect the quality ofthe crystallized sugar.

In the manufacture of dextrose by acid hydrolysis of a starch, such ascorn starch, a large amount of inorganic non-sugars is formed as aresult of neutralizing with alkali the free acid (usually hydrochloricor sulfuric) in the liquor after hydrolysis. The salt formed as a resultof this neutralization constitutes the principal source of inorganicnon-sugars in this case, since the ash constituents of starch areusually quite low. In addition, however, the acid converter liquorresulting from the hydrolysis contains relatively large amounts oforganic impurities such as amino-acids, other proteins, carbohydratesand the like, all of which it would be desirable to remove if practicalbecause of their deleterious effect, as in the case of the inorganicnon-sugars. on the quality and yield of sugar obtained.

In the case of production of sugar from sugar cane, the purification ofthe juice is normally directed particularly to the removal of organiccolloids, defecation being accomplished principally by a relativelysmall dosage of lime, together with one or more of a variety ofspecialclarifying agents which have been introduced in recent years inan effort to improve the vitally important removal of organicnon-sugars. The production of refined white sugar from raw cane sugarfollows much the same general principles.

- It will be apparent from the foregoing discussion that in all casesthe elimination of organic non-sugars, especially organic colloids,constitute an essential step in the purification of sugar juices andsyrups. While there are many ways in which the various organicnon-sugars are objectionable, one of the most obvious is the objectionof color resulting from the presence of certain of these substances;great care and effort therefore are almost universally employed tosecure as complete decolorization as possible.

The removal of inorganic salts or ash constituents, on the other hand,is a consideration the importance of which will naturally vary with theparticular sugar and manufacturing process involved; and it is only inrecent years; that any serious effort has been made to reduce the ashconstituents, even though their deleterious efiect has long beenrecognized, especially in the manufacture of beet sugar.

It has been found that the inorganic salts of beet sugar juice may bereduced practically completely by subjecting the juice to treatmentfirst with a substance having hydrogen-exchange properties and then witha substance having acid-adsorbing properties, Specifically, the ash froma. typical thin juice in one of the important beet sections of theUnited States may be of the order of 4000 to 5000 parts per million. Ofthis amount, about 700 to 1100 parts per million may be composed ofalkaline compounds, principally the carbonates-of potassium, sodium, andcalcium, while the remainder consists mostly of the sulfates andchlorides of potassium and sodium together with inorganic residueresulting from the ignition of metal salts of organic acids. When such ajuice is contacted with a hydrogen exchange body under suitableconditions the salts are converted to the corresponding hydrogencompounds; thus,- the carbonates (and bicarbonates) are converted tocarbonic acid (carbon dioxide and water), the sulfates and chlorides areconverted to free sulfuric and hydrochloric acids respectively, and themetal-organic salts are largely converted to the free organic acids.When subsequently the thus-treated juice is contacted with a body havingacid-adsorption properties, the free sulfuric and hydrochloric acids,and part of the free organic acids, are removed from solution, leavingnothing in their place. In other words, it is possible by this method toremove practically completely the metal salts present in the juice, witha resultant increase in purity the degree and importance of which willbe at once evident to the sugar chemist.

Among the hydrogen exchange bodies suitable for the first step in thistreatment may be mentioned the so-called carbonaceous zeolites, usuallyprepared by the treatment with strong sulfuric acidof wood, lignite,coal or the like, in methods well-known to the art; suitable also arethe cation-exchange synthetic resins, such as the condensation productsof polyhydric phenols and formaldehyde described by Adams and Holmes inthe Journal of the Society of Chemical Industry,-January 11, 1935, Thesehydrogen exchange bodies, preferably employed in beds of granularmaterial through which the liquidto be treated is passed, areregenerated with a solution of a strong acid, such as sulfuric orhydrochloric acid.

Among the acid-adsorption or acid-removal bodies (frequently called alsoanion-exchange I bodies) may be mentioned them-phenylene-diamine-formaldehyde resins, aniline-aldehyde resins andother resins also described by Adams and Holmes (loc. cit.) and byseveral other recent authors and patentees. Inorganic acid-adsorbentshave also been proposed, particularly such as the oxides of iron andaluminum in the form of gels or other highly porous structures.

Similarly, in the case of the manufacture of dextrose from starch, ithas been proposed to lower the ash content of the neutralized converterthetic resins or other acid-removal substances Just described.

The present application is not concerned broadly with the methods ofsugar purification just described and I make no broad claim to suchmethods. My invention is concerned with novel improvements in these andsimilar methods which have been found to increase their utility andliquor by treating the acid liquor before neutralization with anacid-adsorbing body for the removal of free mineral and organic acids,thus making neutralizing unnecessary and consequently avoiding the largeamount of salt heretofore formed as a result of the neutralization. Inthis case, obviously, the free acid to be removed is already present,and does not have to be formed by a hydrogen exchange step. It has beenproposed to utilize for this acid adsorption the syneconomy to such amarked degree that in several cases for the first time the commercialpracticality of such methods is definitely assured.

One of the principal obstacles, as previously noted, to the completeelimination of non-sugars from juices, syrups, etc., is the difficultyof removing from them certain of the organic colloids and other organicsubstances, among which may be mentioned particularly those impartingcolor to the liquids. The effect of some of these impurities is out ofall proportion to the actual weight present. Any practical method forbringing about the more complete removal of these substances istherefore an accomplishment of great importance and utility.

I have found that this result may be accomplished by interposing betweenthe hydrogen exchange treatment and the acid-adsorbing treatment,described in detail above for the treatment of beet juice, a step inwhich the liquid is contacted while in the acid condition with an activecarbon, preferably a decolorizing carbon. An activated carbon of thedecolorizing type is especially suitable. I prefer to use the carbon ingranular form and in a bed through which the acidic sugar liquor ispassed, color and other organic colloids and organic dissolvedimpurities being removed in the passage. The size of the carbonparticles should generally be as small as hydraulic and other operatingconditions will permit in order to provide maximum surface of the carbonparticles per unit of volume. I have found a particle size of 20 to 40mesh, for example, quite satisfactory for several types of this work,although there is obviously considerable latitude in this respect. Thedepth of bed is likewise subject to considerable variation depending oncircumstances. In most cases, however, I prefer to employ a depth of bedfrom about 2 to 4 feet; while there is a cumulative and disproportionateincrease of adsorbent capacity with increased depth of bed up to acertain point, structural and operating considerations are usuallylimiting factors so that it may sometimes be found desirable to employtwo or more comparatively shallow beds in series rather than one bed ofexcessive depth. 7

The rat of flow to be employed in passing the liquid through the carbonbed will naturally vary with each particular set of conditions, and willdepend chiefly on the amount of impurity to be removed, the depth ofcarbon bed, the size of the carbon particles, and similar factors. With20 to 40 mesh carbon particles in beds of 2 to4 feet in depth, rates offlow from 1 to 4 gallons per square foot per minute will satisfactory;

The carbon bed interposed between the hydrogen exchange treatment andacid-adsorbing generally be found the acid-adsorbent bed and make itinactive and unsuitable for use even after the usual regeneration withalkali. The synthetic resins employed for acid-adsorption nowcommercially available are quite expensive, costing from ten to twentytimes as much as activated carbon. It follows that replacement of abedof such syn-- thetic resins constitutes a very substantial item ofoperating expense, whereas the replacement of a bed of activated carbonwould not be a serious handicap even if replacement was necessarycomparatively frequently.

Frequent replacement of the activated carbon bed is not necessary,however, in carrying out the improved process of my invention; for Ihave discovered that if the carbon is used to adsorb organic colloidsfrom sugar juices while these are definitely acid, that is, with a pHsubstantially less'than '7, and preferably less than about 4.3,

the spent carbon bed may be reactivated quite successfully and a greatmany times by simple treatment with a solution of an alkali, preferablysodium or potassium hydroxide or carbonate, as for example, a one-halfto five per cent solution of sodium hydroxide. For example, I have foundin certain cases. that 30 gallons of 1% caustic soda solution per cubicfoot of carbon bed accomplishes effective regeneration for a largenumber of cycles; and in favorable conditions much smaller amounts ofalkali will suflice. In a case in point, the activated carbon bed hadbeen used to decolorize approximately 300 gallons of juice per cubicfoot of carbon in each cycle before regeneration with the alkalisolution.

A particularly useful and economicalmethod of reactivating the spentactivated carbon bed withalkali is to employ all or part of the samealkaline solution that has previously been employed for regenerating theacid-adsorbing body such as the synthetic resins already mentioned. Inthis way the excess alkali (frequently 30 to 50 per cent of the totalalkali) used in regenerating the acid-adsorbing body is utilized inreactivating the carbon, thus saving not only alkali but water as well-afactor frequently of considerable importance, particularly where thedisposal of waste liquids is a problem.

As a specific example of what has actually been accomplished in thisfield, I may mention the purification of a highly colored beet thinjuice (Brix about 11) having the essential inorganic chemicalcharacteristics of the juice above mentioned-that is, an ash of 4000 to5000 parts per million, total alkalinity of 700 to 1000 parts permillion, hardness of 75 to 100 parts per million (the last two valuesbeing expressed in terms of calcium carbonate), sulfate about 300 partsper million, and chloride about 40 parts per million. After I subjectionto hydrogen exchange treatment with a carbonaceous zeolite (sulfonatedcoal) regenerated with sulfuric acid, the pH of the juice was aboi1t2a3at the beginnin and during most of the run; it eventually began to riseand the run was cutoff at a pH of about 3.0 when the conversion of theinorganic and organic salts to the corresponding free acids wasevidently ceasing to be complete. The eilluent from the hydrogenexchange treatment was passed continuously through a bed of granularDarco" decolorizing carbon and then through a bed of syntheticacid-adsorbing resin. The carbon reduced the color of the juice passedthrough it from an intense straw color to practical waterwhiteness.

Ihe purity of the juice entering the three-stage of exceptionally highquality, but also practically the complet elimination of molasses.

The activated carbon bed used in these tests was repeatedly reactivatedin series with the acid-adsorbing resin by the spent alkali solution percent sodium hydroxide) used first for regenerating the resin. Sosuccessful was this method of reactivating both acid-adsorbing resin andactivated carbon in pilot plant operation that at the end of 100 cyclesboth units were operating with the same capacity and efilciency as whennew.

Tests made in the laboratory showed conclusively that when the acidicsugar juices were decolorized by passing through the bed of granularactivated carbonin the manner above described, and the bed subsequentlyactivated with alkali (e. g. sodium hydroxide) the color removed fromthe carbon by the reactivation was equal to that removed from the juice,proper pH correction of the spent regenerant being made to provide afair basis for comparison.

-Prior to regeneration the carbon is preferably drained and washed witha minimum volume of water, the washing having the twofold purpose ofloosening and cleansing the bed and also removing sugar that may berecovered. The alkali regenerating solution maybe applied to the carboncold or hot. A hot solution is sometimes more effective. The time ofapplication may be varied, but I have usually found a period of 15 to 30minutes to beefiective. After the application of alkali the bed is againwashed with water. Many decolorizing carbons have a decided tendency toretain alkali, especially the hydroxides, rather tenaciously, thusprolonging the washing operation: I have found it possible to shortenthis washing period when desirable by treating the carbon with an acidicsubstance, such as sulfuric or hydrochloric or other strong acid, butpreferably carbon dioxide in the form of carbonated water or viouslyregenerated the acid-adsorbing body also,

may be treated'in appropriate manner for recovery of substancescontained inthe liquid.

The activated carbon may be employed also in powdered form in theprocesses of my invention; but it will be obvious that the use of bedsof granular carbon fits in much more conveniently in the three-stagepurification system just described.

I am aware, of course, that active carbon in the form of bone-black,activated carbon and the like has been used for a number of years in thepurification of the juices and syrups of beet sugar, cane sugar, cornsugar and the like, and I make no claim to such broad use. My method ofutilizing active carbon in sugar purification, however, differsradically from those of the prior art in many respects. For example, allprior use of activated carbon in beet sugar manufacture has been in thehighly alkaline pH range characteristic of treated beet juices beforeevaporation, the range being typically from pH 9 to 10. This high pHrange results naturally from the large dosages of lime used inprocessing the juice,

and is lowered only to a limited extent by the carbonation (andsulfitation) steps. As a matter of fact, a. high pH in the juice isdeliberately and carefully maintained, even to the point of addingalkali at various points along the line, if necessary, in order to avoidinversion of the sucrose.

Similarly, in the case of cane Juice and dextrose converter liquor theliquids are quickly brought to a pH of at least 7, and usually between 7and 8.5 before powdered activated carbon is appliedalthough obviously inthe case of the dextrose, the pH of at least 7 is maintained forpurposes "other than that of preventing the inversion of sucrose whichis so carefully cane sugar and beet sugar.

I have found that activated carbon functions much less efiiciently' forthe removal of color and other colloidal substances from sugar Juices inthe high pH environment that characterizes presguarded against with cutpractice, and that the removal proceeds much more satisfactorily if thepH of the liquid is substantially less than 7, and preferably less thanabout 4.3. In other words, the present methods of employing activatedcarbon in sugar purification are diametrically opposed to efilcientutilization of the carbon. As a matter of fact, the high pH of the sugarliquor especially in the case of beet sugar liquors, actually tends toprevent rather than promote adsorption by the carbon. Strikingconfirmation of this statement is found in the fact that the bed ofgranular activated carbon employed in the processes of my invention forthe removal of organic substances from acidic sugar liquors may bereactivated quite eflectively by a very dilute alkali solution, forexample a one-half per cent sodium hydroxide solution. It will thus 7 beseen that, in addition to the particular use-of carbon in the polystagetreatment of sugar juices and syrups herein described, my method ofutilizing the carbon for sugar purification is basically new both in itsapplication to acidic liquors and to its subsequent and cyclic use andreactivation with alkali.

This method'is perfectly practical even in the case of sucrose becausethe low pH. at which adsorption by the carbon takes place is almostimmediately increased to a safe value by the acidadsorption step whichfollows, thus avoiding any loss whatsoever from inversion. If for anyreason, it is desiredstill further to increase the pH of the liquid thathas been treated by the acid-- adsorption body, this result maybeaccomplished by the addition (preferably after removal of carthe liquorby boiling or aera-- bon dioxide from tion) of an extremely small amountof an alkali, such as sodium hydroxide, as the liquor by this time hasbeen freed almost completely of buffering substances.

The basic principles of my invention may be modified in many details formost advantageous adaptation to a specific problem or set of conditions.Thus, in the case of sugar solutions of such initial low ash contentthat decrease of this ash is relatively unimportant, the benefit oftreating with active carbon the sugar liquor in acidic condition may besecured simply by adding the requisite amount of acid as such, as forexample, sulfuric, hydrochloric,'or acetic acid, rather than through thepreviously described. In such cases acidification is carried out to a pHsubstantially less than '1,

mechanism of hydrogen exchange bed of the hydrogen exchange 2,sss,222

and preferably less than about 4.3. The acidic liquor, after-treatmentwith'the active carbon, is then treated for removal of freeacid, as bycon tact with one of the anion-removal bodies previously mentioned, orby direct neutralization with an alkali, or in some cases by simpleboiling or aeration in the event that a readily volatile acid has beenemployed for the acidification.

Other modifications of the basic processes of my invention will besuggested to those skilled in the art on reading of this specification.Alternative or equivalent materials may be employed. as for example,types of acid-adsorbing bodies or of active carbon other than thosespecified. All such modifications are contemplated as coming within thescope of the invention as defined in the appended claims.

I claim: r

1. A process for the purification of a sugar bearing solution whichcomprises contacting the solution successively with'a hydrogen exchangebody, with an active carbon, and with an acidadsorbing body.

2. A process for the purification of a sucrose solution which comprisesconverting dissolved salts to corresponding free acids by hydrogenexchange treatment, removing colloids from the thus-acidified liquor bytreatment with active 5 carbon, and subsequently removing the free acidsby treatment with an acid-adsorbing body. 3. A cyclic process for thepurification of a sugar bearing solution which comprises passing thesugar bearing solution through a bed of a hydrogen exchange material,then through a bed of active carbon and finally through a bed of an acidadsorbing material, and regenerating the material'by passing a dilutesolution of a strong acid therethrough, and the beds of acid adsorbingmaterial and active carbon by passing a streamof a dilute solution ofalkali first through the acid adsorbing material .and then through theactive carbon.

4. The process according to claim 1 in which the hydrogen exchange body,the active carbon and the acid-adsorbing body are all in granular form.

5. In combination with a process for the purification ,of a sugarsolution which comprises .'contacting the solution successively with ahy- 6. A process as described in claim 5 in which the acidic substancecomprises carbon dioxide.

7. The process for the purification ofa sugar solution containingorganic and inorganic impurities, which comprises contacting thesolution with a hydrogen exchange body to exchange H+ for cations ofsalts in said solution, said exchange body being inherently capable offorming acid in said sugar solution as said cations in said solution areexchanged, and powdered active carbon to remove color from saidsolution, and finally contacting said sugar solution with anacid-adsorbing body.

8. In the process for the purification of a sugar bearing solution whichincludes contacting a solution successively with a hydrogen exchangebody and an acid adsorbing body, the improvement which-comprisestreating the solution comand thereafter wash-- ing from the hydrogenexchange body with an active carbon prior to the said treatment with theacid adsorbing body.

9. In the method of refining a sugar bearing solution which comprisesclarifying the solution to remove impurities, and subjecting the thusclarified solution to the sequential exchange action of a bed ofhydrogen exchange material and a bed of acid adsorption material, theimprovement which comprises subjecting the solution coming from thehydrogen exchange bed to treatment with an active carbon prior totreatment with the acid adsorption material.

10. A process for the purification of a sucrose solution which'comprisestreating the solution with a hydrogen exchange body to convert thedissolved salts to thecorresponding free acids and reduce the pH of thesolution to between 4.3 and 7.0, removing colloids from the thusacidified liquor by treatment with active carbon, and subsequentlyremoving the tree acids by treatment with-an acid adsorbing body.

solution which comprises converting dissolved salts to correspondingtree acids by hydrogen exchange treatment, removing colloids from thethus acidified liquor by treatment with active carbon, subsequentlyremoving the free acids by treatment with an acid adsorbing body, andregenerating the spent active carbon with a solution of an alkalipreviously employed for regeneration of the acid adsorbing body.

' ABRAHAM SIDNEY BEHRMAN.

